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Power/Watts: Independent of Pedal Speed?

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Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Power/Watts: Independent of Pedal Speed?

Old 10-18-17, 02:13 PM
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Originally Posted by DaveLeeNC
This may not be a cadence selection thing at all (the highest slopes correlating with the lowest cadence). It is quite likely that these guys just don'e have a gear that will allow them to climb a 15-20% grade at 100 rpm.

dave
Good point dave...or...these guys were on triples and since they live and die by data, they deliberately slowed their cadence to throw off the competition.
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Old 10-18-17, 02:17 PM
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Originally Posted by redlude97
Thanks for the graphs, it means a lot more coming from someone with your experience. My personal experience mirrors theirs albeit at a much lower power output
I don't want to take too much credit. I have it on high authority graphs shown started life as a Rorschach test and then was decided that scale would be added to abscissa and ordinate to create a quantitative analysis.
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Old 10-18-17, 03:28 PM
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Originally Posted by DaveLeeNC
This may not be a cadence selection thing at all (the highest slopes correlating with the lowest cadence). It is quite likely that these guys just don'e have a gear that will allow them to climb a 15-20% grade at 100 rpm.

dave
Right, I think cadence is a dependent (aka endogenous), not an independent (exogenous), variable. I think riders decide the speed they need to keep up in the race and that implies a certain amount of power. They can achieve that power either by changing their cadence or their crank torque or both -- but in the data I've seen they *mostly* modulate their power by varying their crank torque.

Here's a plot from a different rider on a different hill. The hill was about 15 minutes long, and I snipped away the rest of the ride to focus only on that hill. The top two panels show the relationship between power and cadence, and power and crank torque. The two bottom panels show the relationship between cadence and torque. As it happens I can see his choice of gearing at each second of the climb, and the lowest ring-cog combo he used was a 39/23 although he had a 39/25. I think you can see that the relationship between crank torque and power is much stronger than the relationship between cadence and power -- that means this rider is *mostly* using crank torque to modulate his power.

The bottom right panel shows you how the combinations of cadence and crank torque he used were related to his power.


Last edited by RChung; 10-18-17 at 03:32 PM.
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Old 10-19-17, 05:07 PM
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Originally Posted by RChung
...in the data I've seen they *mostly* modulate their power by varying their crank torque.
...
I bought one of these CVT/infinite gear bikes for tooling around on and kid's school commute. The bike was heavy and not fun to ride, but changing gear ratio was a very easy turn of the handle, like a motorcycle accelerator. I noticed (no power meter) that I was turning my wrist for little things where I may have just torqued through it.

I wonder if the data you see is not more just because the shift takes some mental energy/guess work and is often too big, where the rider can do a mini stomp on the pedal and get the same result.
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Old 10-19-17, 05:13 PM
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This thread is awesome. OP question answered in the first 2 posts and its still going 6 pages later!
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Old 10-19-17, 06:05 PM
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Originally Posted by Dean V
This thread is awesome. OP question answered in the first 2 posts and its still going 6 pages later!
The first two posts neglected physiological efficiency, and that's where most of the arguing comes in.
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Old 10-19-17, 06:45 PM
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Originally Posted by Doge
I bought one of these CVT/infinite gear bikes for tooling around on and kid's school commute. The bike was heavy and not fun to ride, but changing gear ratio was a very easy turn of the handle, like a motorcycle accelerator. I noticed (no power meter) that I was turning my wrist for little things where I may have just torqued through it.

I wonder if the data you see is not more just because the shift takes some mental energy/guess work and is often too big, where the rider can do a mini stomp on the pedal and get the same result.
Put some Vectors or P1's on your CVT bike and tell us what you find.
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Old 10-19-17, 10:26 PM
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Originally Posted by RChung
Put some Vectors or P1's on your CVT bike and tell us what you find.
Likely not because:
Originally Posted by Doge
... The bike was heavy and not fun to ride, ..
And I don't have pedal PMs.
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Old 10-19-17, 10:33 PM
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Originally Posted by wphamilton
The first two posts neglected physiological efficiency, and that's where most of the arguing comes in.
OP wasn't asking about that. Just the basic physics.
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Old 10-20-17, 05:49 AM
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Originally Posted by Dean V
OP wasn't asking about that. Just the basic physics.
Physiological efficiency is part of the basic energy equation.

Drive efficiency varies according to the gear selected - I'm not sure that's even been mentioned yet but should also be part of the answer.
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Old 10-20-17, 10:03 AM
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Originally Posted by Doge
Likely not because:


And I don't have pedal PMs.
Then do the opposite: with your existing bike and existing PM,
1) collect data while riding up a hill while shifting normally; then
2) repeat on the same hill while shifting like mad; then
3) repeat on the same hill while keeping the bike in one single gear.

Then see how much the cadence/torque/power relationships vary across your three runs.
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Old 10-20-17, 10:49 AM
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Originally Posted by wphamilton
Physiological efficiency is part of the basic energy equation.

Drive efficiency varies according to the gear selected - I'm not sure that's even been mentioned yet but should also be part of the answer.
Read the original question:

Power/Watts: Independent of Pedal Speed?
Probably a basic physics question. Is wattage affected by cadence? If, say, two identical riders on identical bikes are riding together, same speed; one is in a large gear pedaling at ~70rpm, while the other is spinning at 110+rpm. Is one producing more watts than the other?
Nowhere does the OP ask anything about which rider produces the energy more physiologically efficiently.
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Old 10-20-17, 11:28 AM
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Originally Posted by caloso
Read the original question:



Nowhere does the OP ask anything about which rider produces the energy more physiologically efficiently.
"Is one producing more watts than the other?"

You, and others apparently, are assuming that this can only mean power at the crank, propelling the bike forward. That assumption is incorrect, and not just technically. He wanted to know if there is any difference in regards to the power a given rider can provide, given different cadences.

Obviously, if you could provide 250 watts for an hour at 80 rpm, and only 200 watts for an hour at 140 rpm, you would have to agree that you produce more watts at the 80 cadence. The situation is nowhere near that drastic, but where there IS even a small difference, it is precisely what he was asking.
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Old 10-20-17, 11:37 AM
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Again, you are reading into the question and adding words the OP did not use. Look at the sentence you quoted. It is "Is one producing more watts than the other?"

Not "Is one [more physiologically efficient such that he is capable of] producing more watts than the other [over a given time]?" Which is an entirely different question you seem to be trying to answer.

I'm not saying you and others are wrong, just that it is literally not the question asked.
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Old 10-20-17, 11:53 AM
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Originally Posted by caloso
Again, you are reading into the question and adding words the OP did not use. Look at the sentence you quoted. It is "Is one producing more watts than the other?"

Not "Is one [more physiologically efficient such that he is capable of] producing more watts than the other [over a given time]?" Which is an entirely different question you seem to be trying to answer.

I'm not saying you and others are wrong, just that it is literally not the question asked.
Two things.

If I have expended 800 kilojoules for an hour, and you have expended 1000 for an hour, yet both of our power meters read 250 watts, which of us produced more power?

Secondly, if my drive loses 5% power between the crank and the ground, and your's loses 2%, and both of our crank meters read 250 watts, which of us produced more power?

If he wanted a simple physics answer to torque/cadence/power that's one thing. From the OP post I infer two questions. IS it a basic physics question (no), and what effect does cadence have on power? Do the crank meters read the same - yes, presuming that they're accurate. Include cyclists in the scenario, as he does, well then there's a difference.
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Old 10-20-17, 12:01 PM
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I dont buy the "higher rpm is more efficient" dogma. Try Spinning at 120 rpm on a very light load compared to 80 rpm. At 120 you spend a lot of energy just moving yous legs up and down, spinning the crank, even without doing any real work (moving the bike). Just try it out and you'll see.
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Old 10-20-17, 12:18 PM
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Originally Posted by Racing Dan
I dont buy the "higher rpm is more efficient" dogma. Try Spinning at 120 rpm on a very light load compared to 80 rpm. At 120 you spend a lot of energy just moving yous legs up and down, spinning the crank, even without doing any real work (moving the bike). Just try it out and you'll see.
The point of high RPM isn't energy/oxygen efficiency, it's reducing torque to keep the leg muscles from exploding.

(Similarly, the point of high torque is to avoid spinning out. The body has a lot of bottlenecks, and it's all a balancing act.)
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Old 10-20-17, 12:26 PM
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Originally Posted by wphamilton
Two things.

If I have expended 800 kilojoules for an hour, and you have expended 1000 for an hour, yet both of our power meters read 250 watts, which of us produced more power?

Secondly, if my drive loses 5% power between the crank and the ground, and your's loses 2%, and both of our crank meters read 250 watts, which of us produced more power?

If he wanted a simple physics answer to torque/cadence/power that's one thing. From the OP post I infer two questions. IS it a basic physics question (no), and what effect does cadence have on power? Do the crank meters read the same - yes, presuming that they're accurate. Include cyclists in the scenario, as he does, well then there's a difference.
Two things:

1) You are conflating power and energy. They are related but different. Energy measures the work that's delivered. Power measures the rate at which it is delivered.

2) He literally asked a simple physics question and you inferred a more complicated question than the one posed.

Again, I'm not saying you are wrong; just that the question was asked and answered several times in the first 10 posts, yet this thread has gone on for many pages arguing about a question that wasn't asked. It may be a related question; it may be a more interesting question; but it's not the question originally asked.

Which makes this thread a leading contender for 41-iest Thread of the Year.
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Old 10-20-17, 01:09 PM
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Originally Posted by HTupolev
The point of high RPM isn't energy/oxygen efficiency, it's reducing torque to keep the leg muscles from exploding.

(Similarly, the point of high torque is to avoid spinning out. The body has a lot of bottlenecks, and it's all a balancing act.)
I get what the supposed idea is, however I find I tire faster above 85-90 rpm or so, which is consistent with the finding, that just spinning the crank at high rpm is tiring even if no real work is produced.
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Old 10-20-17, 01:14 PM
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Originally Posted by patrickgm60
Probably a basic physics question. Is wattage affected by cadence? If, say, two identical riders on identical bikes are riding together, same speed; one is in a large gear pedaling at ~70rpm, while the other is spinning at 110+rpm. Is one producing more watts than the other?
No, the power at the crank is the same, but one rider may tire faster than the other, even if they are identical, due to the physiologic effects of riding a different cadences. The debate then, is what cadence is the best. The answer to that question is, Imo, it depends ... :-)
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Old 10-20-17, 01:17 PM
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Originally Posted by caloso
Two things:

1) You are conflating power and energy. They are related but different. Energy measures the work that's delivered. Power measures the rate at which it is delivered.
No, "1000 kilo-joules in an hour" IS power (278 watts in fact), no conflation going on there. There seems to be a blind spot with cyclists, maybe because the conversion of kj - calorie is so close to metabolic efficiency, that they don't think of the efficiency changing under different conditions.

Originally Posted by caloso
2) He literally asked a simple physics question and you inferred a more complicated question than the one posed. Again, I'm not saying you are wrong; just that the question was asked and answered several times in the first 10 posts,
Not trying to be picky, but he literally asked if it WAS a simple physics question. It's only a simple physics answer if you ignore the variables. To put it bluntly, only kbarch got it close to right, and he also neglected that drive train efficiency is also part of the "simple physics" answer (which invalidates ALL of the first 10 answers).
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Old 10-20-17, 01:20 PM
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Originally Posted by Racing Dan
No, the power at the crank is the same, but one rider may tire faster than the other, even if they are identical, due to the physiologic effects of riding a different cadences. The debate then, is what cadence is the best. The answer to that question is, Imo, it depends ... :-)
But what about at the wheel
A lower cadence and/or a better chainline will have lower drivetrain friction losses
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Old 10-20-17, 01:23 PM
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Originally Posted by redlude97
But what about at the wheel
A lower cadence and/or a better chainline will have lower drivetrain friction losses
Yeah, what about the air friction from rotating the crank faster ...
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Old 10-20-17, 03:26 PM
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Originally Posted by Racing Dan
I dont buy the "higher rpm is more efficient" dogma. Try Spinning at 120 rpm on a very light load compared to 80 rpm. At 120 you spend a lot of energy just moving yous legs up and down, spinning the crank, even without doing any real work (moving the bike). Just try it out and you'll see.
I just tried it and hit my knee on the desk.
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Old 10-20-17, 04:04 PM
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Originally Posted by wphamilton
"Is one producing more watts than the other?"

You, and others apparently, are assuming that this can only mean power at the crank, propelling the bike forward. That assumption is incorrect, and not just technically. He wanted to know if there is any difference in regards to the power a given rider can provide, given different cadences.

Obviously, if you could provide 250 watts for an hour at 80 rpm, and only 200 watts for an hour at 140 rpm, you would have to agree that you produce more watts at the 80 cadence. The situation is nowhere near that drastic, but where there IS even a small difference, it is precisely what he was asking.
I am agreeing with you.

The other thing closely associated with this is how much energy it takes to produce those watts.
To your example - Junior gears in adult races. I've always argued that the kids having to spin 140 where the adults spin 100 was unfair. People post back it does not really matter, and you just need to learn to spin. I never see a road cyclist spinning 140 when they have the opportunity to shift - they do.
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